Superconducting components are used in many applications including the determination of magnetic susceptibilities of tiny samples on a wide temperature range. The detection of nuclear magnetic resonance and quadripolar resonance, the measurement of temperature by means of noise measurements (also called noise thermometry), biomagnetism, geophysics, magnetism of rocks or paleomagnetism.
For this, one makes use of the Josephson affect. By definition, the Josephson affect is made manifest by the occurrence of a current, also called a super-current, between two superconducting materials separated by a layer formed with an insulating or non-superconducting metal material. The assembly of both superconducting materials and the layer is called a “Josephson junction”.
The occurrence of this current is explained by the macroscopic theory of superconductivity developed by John Bardeen, Leon Cooper and Robert Schrieffer. According to this theory, above the superconducting transition temperature, at least one portion of the free electrons in the superconducting material are bound together so as to form pairs of electrons so-called “Cooper pairs”.
Super-conductivity is a macroscopic quantum phenomenon inducing order at a macroscopic scale, which has three main consequences: infinite electric conductivity of a superconducting ring justifying the existence of a permanent current of Cooper pairs, the quantification of the magnetic flux through a superconducting ring, resulting from the application of a magnetic field and of the current induced into the ring and the Josephson affect sometimes called a Josephson tunnel affect. In order to explain the latter phenomenon, let us consider two super-conductors separated by a thin insulating barrier through which the Cooper pairs may pass by a quantum tunnel affect, by maintaining the phase coherence between both super-conductors during the method. Josephson showed that the difference δ between the phases of the wave functions on both sides of the Josephson junction is in relationship with a super-current I circulating through the barrier and at the voltage V on the terminals of the Josephson junction by the following relationship:
      {                                                      sin              ⁢                                                          ⁢              δ                        =                          I                              I                C                                                                                      V            =                                                            Φ                  0                                                  2                  ⁢                  π                                            ⁢                                                ∂                  δ                                                  ∂                  t                                                                          }     
Wherein:                IC is the critical current, which is the maximum super-current which the Josephson junction may support; this critical current is related to the transparency of the barrier and to the Cooper pair density in the Josephson junction, and        Φ0 is the flux quantum, which is the ratio between Planck's constant and the charge of a Cooper pair.        
In a Josephson junction, the current of Cooper pairs contributes to electron transport, but in parallel, there conventionally exists the current of lone electrons («quasiparticles») associated with a dissipative term characterized by a resistance Rn. From this results a differential equation of the first order in δ, which may be analytically solved for obtaining the time-dependent change in δ, which gives after a time average, the following equation:
      〈    V    〉    =                              Φ          0                          2          ⁢          π                    ⁢              〈                              ∂            δ                                ∂            t                          〉              =                  V        C            ⁢                                    I            2                    -                      I            C            2                              
Wherein VC=Rn. IC is the characteristic voltage of the Josephson junction.
It is desirable to propose arrangements of superconducting components giving the possibility of benefitting from this property like superconducting loops comprising a quantum interference superconducting device, most often designated under the acronym of SQUID, which refers to “Superconducting Quantum Interference Device”. Such a SQUID is a superconducting loop provided with one (respectively two) Josephson junction(s) operating with a radiofrequency current (respectively a direct current). Obtaining that the thickness of the superconducting loop of a super-conductor circuit should be high, in order to obtain a low inductance while having a thin Josephson junction thickness so that the normal resistance is high.
From the state of the art, it is thus known how to make relatively complex superconducting circuits in two dimensions by producing the Josephson junction barrier by localized irradiation of oxygen or fluorine ions.
A low dose of irradiation gives the possibility of obtaining a Josephson junction which may operate at a temperature of the order of 70 K (Kelvins), but having a low normal resistance (a few tens of Ohms). Such a resistance is generally considered to be too small.
A strong dose of irradiation or an increase in the thickness of the barrier gives the possibility of increasing the resistance of the Josephson junction. However, this imposes operation at lower temperatures, for example between 30 and 40 K, which is a constraint.